The Real Science of Avatar

On Pandora: Hallelujah Mountains
Pieces of these mist-covered, mesa-like mountains rip loose and float in the sky, like icebergs in the ocean. Waterfalls flow from the peaks, and straggly vines and ferns dangle off the sides. The humans in Avatar coined these the "Hallelujah Mountains" because they're a source of unobtainium, a mineral sought after as a solution to Earth's energy crisis.

• In Honor of Earth Day: The Earth from Above